The electronic and optical performances of P-PPV light-emitting diodes with lithium fluoride insulating layer between the metal cathode and active polymer are studied. As for the polymer light-emitting diodes

optimization of charge injection lies in the dominant factors for substantive improvement performance. Since the minority carriers dominate the recombination thus the radiation

their injection takes priority over that of (majority) carriers. Generally in semiconducting polymers

holes are majority carriers while electrons are the (minority

) the carrier misbalance between electrons and holes further deteriorate in the fact that holes usually take possession of higher mobility and smaller injection barrier. To balance injection charge carriers and facilitate the (electron) injection

there are two commonly stratagems to be used in cathode fabrication. One is to employ low work function metals such as barium and calcium as cathode though they are susceptible to degradation upon water vapor and oxygen. The other choice is proposed to insert an insulating thin layer of lithium fluoride (between) polymer/electrode interfaces to build a bilayer cathode. As shown by the experiment results

the LiF/Al double-layer-cathode with Ba(Ca)/Al electrode devices can improve in luminescence performance. Band bending and injection potential decrease of minority carrier caused by the inlay of metal fluoride insulating (layer

) which is proposed to be responsible for the enhanced electron injection and improved performance in polymer light (emitting ) diodes.